The present invention relates generally to a process for optimizing the storage capacity, based on weight, of a hydrogen storage device containing a hydride-forming alloy, and to a corresponding hydrogen storage device.
Hydrogen storage devices which are currently in use and in which hydrogen is stored in a hydride-forming alloy contain for example such hydrogen-storing alloys as TiFe hydrides or hydrides of the C 14 Laves phase (crystal structure), which have a storage capacity for H.sub.2 of between about 1.6 and 1.9% by weight, based on the alloy. Such crystal structures are well-known in the prior art and are discussed in more detail in scientific reference works such as Roempps Chemical Dictionary and D'Ans Lax Handbook of Chemistry and Physics, Volume 1, pp. 629-631. When 3d transition metals (i.e., those having incomplete orbitals or exhibting a tendency to form one or more cations having incomplete orbitals) are used, the hydrogen capacities are between about 1.8 and 3% by weight, based on the alloy material and depending on the operating pressures and the discharge temperatures. Preferred alloy compositions are disclosed in U.S. Pat. No. 4,446,101 and DE-PS No. 32 10 381 which are hereby incorporated by reference.
The hydrogen storage devices which contain these storage alloys are currently designed to operate under a pressure of about 50 bars. The hydride loading weights are about 3 to 4 kg per liter when hydrides based on the 3d transition metals are used. Loading weights are understood as meaning the weight of storage alloy which is present in the storage device, per liter of hydrogen storage volume. When other storage alloys are used, the loading weights vary according to the atomic or molecular weights.
The storage capacities effectively to be achieved in these storage devices are about half the storage capacity of the storage alloy, based on the weight of the total storage device. For example, with TiFe hydrides or hydrides of the C14 Laves phase, which store between 1.6 and 1.9% by weight of hydrogen, based on the alloy, effective capacities of only 0.8 to 1.0% by weight, based on the total weight of the storage device, are achieved.
An object of the present invention is the provision of a Process which optimizes the storage capacity, based on weight, for hydrogen, so that more hydrogen than before can be stored per unit weight of the storage device.
Another object of the present invention is the provision of a storage device for optimized storage of hydrogen.
These and other objects of the present invention are attained by the provision of a process for optimizing storage capacity of a hydrogen storage device containing a hydride-forming alloy and a hydrogen storage device corresponding thereto. The hydrogen storage device is partially filled with a hydride-forming alloy which contains at least 0.8 kg of hydride-forming alloy per liter of internal volume and preferably about 0.8-2 kg of hydride-forming alloy per liter to a volume. The container is then charged with hydrogen gas of a pressure of at least 100 bars and preferably to a pressure of between 100 and 300 bars. The corresponding hydrogen storage container is designed to accommodate such pressures and to hold the requisite quantity of hydride-alloy per liter of internal volume.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings, which show for purposes of illustration only, an embodiment constructed in accordance with the present invention.